Unlike those who suffer more severe concussions, mild brain injury victims may have no immediate outward symptoms of the damage their brains have sustained -- even though this damage could put them at greater risk of bigger problems later.

For this reason, all too often, mild concussions go undetected, exposing the person to much more serious brain damage if they suffer a second concussion before the first one is fully healed.

Most concussions happen to children younger than 4 and to teenagers.

Niki Popyer suffered seven concussions before the age of 14, playing basketball. Now she suffers from dizziness, memory loss and difficulty concentrating.

"I can't go to the movies. I can't ride a train or do anything that could potentially get hit," she said.

And last year, actress Natasha Richardson died of a brain hemorrhage after what at first seemed to be a minor fall on a Canadian ski slope.

Doctors say the idea that they could one day have a test that could quickly warn of the potential for brain damage in the absence of neurological signs is exciting. Brain injury experts, however, said there's still a lot of work to be done to validate and develop a reliable test that will be easy for those in the field -- such as football coaches and ski resort managers -- to use.

Banyan Tests Blood of 34 With Mild Concussions

Lead by Banyan Biomarkers, researchers drew and tested the blood of 34 people taken to the hospital for head injuries and then diagnosed with mild concussions at a trauma unit.

The blood tests showed the presence of certain proteins -- biomarkers -- that do not normally show up in the blood of uninjured people. The theory is that the concussive jolt to the brain unleashes these proteins in the bloodstream.

"We have found very unique, specific proteins that are released into the bloodstream when the brain cells are injured," said Army Col. Dallas Hack, M.D., the director of the Combat Casualty Care Research Program at Fort Detrick, Md.

"Some of those are actually high enough in concentration, they get across into the bloodstream. ... We have been able to, in a series of patients, identify adequate quantities of two of these [proteins] that we can measure them up," Hack said.

If, in fact, the biomarkers found in the subjects' blood turns out to be correlated with their brain injuries, it would be the first suggestion that a blood test to test for brain injury in humans could be a reality. Hack already calls the finding a major breakthrough for researchers who've been seeking for 10 years a blood test that might signal a concussion.

"We've done a lot of work in animals and this is confirmation in people that this actually works," he said. "We're quite certain this will work."

Hack said that the Army has already ordered prototypes of handheld devices that would involve a pin prick to get similar information and could be used in the field.

"We obviously have to do significant clinical trials and get this to the [Food and Drug Administration] so they can approve it," he said.

Experts contacted by ABC News differed in their opinions on the Banyan-Army study.

Experts Opine on Banyan Research

"Banyan Biomarkers has identified some novel biomarkers in CSF (cerebral spinal fluid) and blood that show promise for enhancing the predictive capability as compared to prior biomarkers," said Dr. Alan Faden, director of the Center for Shock, Trauma and Anestesiology Research at the University of Maryland School of Medicine, in an e-mail to ABC News. "But at present there are insufficient data to support the 'hype' expressed by Col. Hack."

"For mild traumatic brain injury or concussion, which represents approximately 90 percent of all traumatic brain injury severity ... the jury is still out," said Dr. Jamshid Ghajar, neurosurgeon and president of the Brain Trauma Foundation. "The CDC (Centers for Disease Control and Prevention) published mild traumatic brain injury guidelines ... in 2008 and evaluated the literature for biomarkers to ascertain whether a concussion patient should get a CT scan. The question asked was if the biomarker could predict which concussion patient had an abnormal CT scan. There was not sufficient evidence to make that recommendation."

"It should be emphasized that this research is very preliminary," said Dr. Allen Brown, associate professor of Physical Medicine and Rehabilitation at the Mayo Clinic in Rochester, Minn. "The clinical definition of 'mild' brain injury has not been sufficiently established."

However, Robert Stern, an associate professor of neurology at Boston University, said Banyan's research held great promise for the early and immediate detection and diagnosis of traumatic brain injury for service members.

"The assessment of biomarkers through a blood test is definitely a feasible and meaningful method of accomplishing this," he said.

Gerald Grant, a Duke neurosurgeon, said the potential value of the test was tremendous. "This is kind of our holy grail," he said. "We really want a biomarker or a series of biomarkers ... that can be very sensitive to pick up these injuries."

A much larger study, funded by the U.S. Defense Department, is expected to begin next year. It will involve 1,200 patients at 30 trauma centers around the country.

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